1. Field of the Invention
The present invention relates to a method of producing a gallium phthalocyanine crystal and a method of producing an electrophotographic photosensitive member using the method of producing a gallium phthalocyanine crystal.
2. Description of the Related Art
Conventionally, a phthalocyanine-based pigment has been attracting attention, and has been investigated, as an electronic material to be used in an electrophotographic photosensitive member, a solar cell, a sensor, or the like in addition to its application for coloring.
An oscillation wavelength of semiconductor laser, which has been frequently used as an image exposing unit for an electrophotographic photosensitive member, is, at present, a long wavelength such as 650 to 820 nm. Accordingly, development of an electrophotographic photosensitive member having high sensitivity to light having such a long wavelength has been advanced.
The phthalocyanine pigment is effective as a charge-generating substance having high sensitivity to light having a wavelength in such a long-wavelength region. In particular, oxytitanium phthalocyanine and gallium phthalocyanine have excellent sensitivity characteristics, and various crystal forms thereof have been reported heretofore.
An electrophotographic photosensitive member using the phthalocyanine pigment has an excellent sensitivity characteristic. However, the electrophotographic photosensitive member involves the following problem. A produced photocarrier is liable to remain on the photosensitive layer of the electrophotographic photosensitive member and is liable to serve as a kind of memory to cause an electric potential variation such as a ghost phenomenon.
The following has also been found. In the case where gallium phthalocyanines each are used in an electrophotographic photosensitive member, changes in electrophotographic characteristics of the electrophotographic photosensitive member significantly occur depending on the differences in production methods such as a raw material and a solvent to be used, and in production conditions such as a reaction temperature and a loading ratio even when the crystal forms of the gallium phthalocyanines are the same. In particular, the resultant electrophotographic photosensitive members significantly differ from each other in sensitivity and chargeability.
Japanese Patent Application Laid-Open No. 2001-40237 reports that addition of a specific organic electron acceptor at the time of an acid pasting process for the phthalocyanine pigment exerts a sensitizing effect. However, the approach involves the following concern and problem. The additive may chemically change, thereby being difficult to transform the additive into a desired crystal form.
In addition, Japanese Patent Application Laid-Open No. 2006-72304 reports the following. When the pigment and a specific organic electron acceptor are subjected to a wet pulverization treatment, the organic electron acceptor is incorporated in a surface of the crystal simultaneously with crystal transformation, and hence the electrophotographic characteristics are improved. However, even in a case where the specific organic electron acceptor is incorporated in the surface of the crystal, it is identical in constitution and effect to the so-called addition at the time of dispersion in which the same organic electron acceptor is added at the time of production of a coating liquid for a charge-generating layer.
As described above, various improvements have been attempted for an electrophotographic photosensitive member.
An additional improvement in sensitivity and the alleviation of deterioration of image quality due to the ghost phenomenon have been desired in association with an increase in print speed and an improvement in quality of a printed image in recent years. However, it has been difficult to achieve compatibility between the additional improvement in sensitivity and the improvement in image quality owing to existence of the following dilemma. When an attempt is made to improve the sensitivity, the ghost phenomenon is exacerbated.